Messages in this thread Patch in this message | | | Subject | Re: [PATCH V5 6/7] i2c: tegra: fix PIO rx/tx residual transfer check | From | Bitan Biswas <> | Date | Thu, 13 Jun 2019 02:59:25 -0700 |
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On 6/12/19 6:55 AM, Dmitry Osipenko wrote: > 11.06.2019 13:51, Bitan Biswas пишет: >> Fix expression for residual bytes(less than word) transfer >> in I2C PIO mode RX/TX. >> >> Signed-off-by: Bitan Biswas <bbiswas@nvidia.com> >> --- >> drivers/i2c/busses/i2c-tegra.c | 11 ++++++----- >> 1 file changed, 6 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c >> index 4dfb4c1..0596c12 100644 >> --- a/drivers/i2c/busses/i2c-tegra.c >> +++ b/drivers/i2c/busses/i2c-tegra.c >> @@ -514,7 +514,8 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev) >> * If there is a partial word at the end of buf, handle it manually to >> * prevent overwriting past the end of buf >> */ >> - if (rx_fifo_avail > 0 && buf_remaining > 0) { >> + if (rx_fifo_avail > 0 && >> + (buf_remaining > 0 && buf_remaining < BYTES_PER_FIFO_WORD)) { > > The buf_remaining >= BYTES_PER_FIFO_WORD is not possible to happen > because there are three possible cases: > > 1) buf_remaining > rx_fifo_avail * 4: > > In this case rx_fifo_avail = 0 > > 2) buf_remaining < rx_fifo_avail * 4; > > In this case buf_remaining is always < 4 because > words_to_transfer is a buf_remaining rounded down to 4 > and then divided by 4. Hence: > > buf_remaining -= (buf_remaining / 4) * 4 always results > into buf_remaining < 4. > > 3) buf_remaining == rx_fifo_avail * 4: > > In this case rx_fifo_avail = 0 and buf_remaining = 0. > > Case 2 should never happen and means that something gone wrong. > Yes I now agree with you. The first condition "rx_fifo_avail > 0" failure will take care and prevent need for additional checks.
>> BUG_ON(buf_remaining > 3); >> val = i2c_readl(i2c_dev, I2C_RX_FIFO); >> val = cpu_to_le32(val); >> @@ -557,11 +558,10 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) >> words_to_transfer = tx_fifo_avail; >> >> /* >> - * Update state before writing to FIFO. If this casues us >> + * Update state before writing to FIFO. If this causes us >> * to finish writing all bytes (AKA buf_remaining goes to 0) we >> * have a potential for an interrupt (PACKET_XFER_COMPLETE is >> - * not maskable). We need to make sure that the isr sees >> - * buf_remaining as 0 and doesn't call us back re-entrantly. >> + * not maskable). >> */ >> buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD; >> tx_fifo_avail -= words_to_transfer; >> @@ -580,7 +580,8 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev) >> * prevent reading past the end of buf, which could cross a page >> * boundary and fault. >> */ >> - if (tx_fifo_avail > 0 && buf_remaining > 0) { >> + if (tx_fifo_avail > 0 && >> + (buf_remaining > 0 && buf_remaining < BYTES_PER_FIFO_WORD)) { >> BUG_ON(buf_remaining > 3); >> memcpy(&val, buf, buf_remaining); >> val = le32_to_cpu(val); >> > > Same as for RX. > Yes shall discard this patch from the next update.
-Thanks, Bitan
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